change master to到一个不存在的主库或主库无法连接

本文测试当主库无法连接时，从库的复制状态。

1.设置主库

在从库上， 将主库设置为//127.0.0.1或一个无法连接的主库：

MASTER_HOST='//127.0.0.1'

或

MASTER_HOST='_'

设置复制：

mysql> stop slave;
Query OK, 0 rows affected (0.00 sec)

mysql> 
mysql> CHANGE MASTER TO MASTER_HOST='//127.0.0.1', MASTER_PORT=3306,MASTER_AUTO_POSITION=1;
Query OK, 0 rows affected (0.01 sec)

mysql> start slave;
Query OK, 0 rows affected (0.00 sec)

2.查看复制状态

mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Connecting to master
                  Master_Host: //127.0.0.1
                  Master_User: rep
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: 
          Read_Master_Log_Pos: 4
               Relay_Log_File: relay-bin.000001
                Relay_Log_Pos: 4
        Relay_Master_Log_File: 
             Slave_IO_Running: Connecting
            Slave_SQL_Running: Yes
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 0
              Relay_Log_Space: 154
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 2005
                Last_IO_Error: error connecting to master 'rep@//127.0.0.1:3306' - retry-time: 60  retries: 1
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 0
                  Master_UUID: 
             Master_Info_File: mysql.slave_master_info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 200129 12:29:28
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 43cf1658-41a4-11ea-9f90-080027974966:1-3
                Auto_Position: 1
         Replicate_Rewrite_DB: 
                 Channel_Name: 
           Master_TLS_Version: 
1 row in set (0.00 sec)

IO线程状态

主库无法连接，连接错误如下所示：

Slave_IO_State: Connecting to master
Master_Host: //127.0.0.1
Master_User: rep
Master_Port: 3306

Slave_IO_Running: Connecting
Slave_SQL_Running: Yes

Last_IO_Errno: 2005
Last_IO_Error: error connecting to master 'rep@//127.0.0.1:3306' - retry-time: 60  retries: 1

可以看到，IO线程正在尝试连接主库。

日志位点信息

由于主库无法连接，日志位点相关的信息如下。

从库已经接收的主库日志位点信息：

Master_Log_File: 
Read_Master_Log_Pos: 4

可以看到，日志文件为空，日志起点从4开始。

已经执行到的主库日志位点信息：

Relay_Master_Log_File:
Exec_Master_Log_Pos: 0

已经执行的relay log信息：

Relay_Log_File: relay-bin.000001
Relay_Log_Pos: 4